An overview of biopolymers is given in G. Ebert, “Biopolymers”, B. G. Teubner, Stuttgart, 1993>and E. S. Stevens, “Green Plastics—An Introduction to the New Science of Biodegradable Plastics”, Princeton University Press, Princeton, N.J., 2002.
Apart from the classification of biopolymers according to their chemical nature, plastic material in general can be divided into thermoplastic, thermoset, and elastomeric materials according to German Industry Standard DIN 7742, part 2 (classification according to the temperature dependence of their modulus of shear deformation).
In the following description of prior art this classification will be used.
Thermoplastic Systems:
The use of biopolymers or compounds from renewable resources that can be processed like thermoplastic materials has been extensively described. In many cases mixtures of natural polymers and synthetic polymers are used to ensure the processability required for compression molding or injection molding.
Frequently used matrix materials in fiber reinforced compounds are thermoplastically processable starch, lignin, and shellac. WO-A-00/27924 teaches the use of lignin and shellac together with natural fibers as a raw material for an injection molding process.
An example of a polymer obtained by polymerization of a native monomer is poly(lactic acid) (PLA). Lactic acid can be polymerized to yield a low molecular weight polymer that can be treated with coupling agents to form poly(lactic acid) (PLA) of higher molecular weight. High molecular weight PLA with better mechanical properties can be obtained via metal-catalyzed ring opening polymerization of the cyclic dimer of lactic acid.
It is known that such thermoplastic materials often suffer from poor mechanical properties, i.e. low tensile and flexural strength and also low tensile and flexural modulus. Moreover, low glass transition temperatures (Tg values) limit their applicability. An overview of the mechanical properties of thermoplastic biopolymers is given by U. Riedel, 1999, “Entwicklung und Charakterisierung von Faserverbundwerkstoffen auf der Basis nachwachsender Rohstoffe” VDI-Fortschrittberichte Reihe 5, Nr, 575, VDI-Verlag GmbH 1999 Düsseldorf.
Thermosetting Systems:
Thermosetting polymers of natural origin are known for a long time, as shellac—which can be processed like a thermoplastic material—can also be polymerized, i.e. show a thermosetting behavior. U.S. Pat. No. 2,010,227 teaches the use of asbestos as fibrous reinforcement and shellac as a thermosetting matrix material that reacts with polycarboxylic acids to yield a composite material which is said to have enhanced mechanical properties and thermal resistance.
U.S. Pat. No. 5,948,706 describes mixtures of shellac with crosslinking agents like oxalic acid, urea, aluminum chloride, ammonium zirconium carbonate, and ammonium compounds. The mixtures are used together with natural fibers like ramie, flax, sisal, jute, and hemp.
There are also examples of thermosetting biopolymeric resin systems on the basis of triacylglycerols which can be processed in a manner similar to conventional thermosetting resins. U.S. Pat. No. 6,900,261 teaches the use of an unsaturated polymer resin on the basis of a natural triglyceride oil in a sheet molding compound application. The triglyceride oil which can stem from soybean, linseed, rapeseed and the like is functionalized with carboxyl groups and/or hydroxyl groups and ethylenically unsaturated groups. The carboxyl groups provide the possibility for thickening reactions as described above. The ethylenically unsaturated functionalities are used for crosslinking reactions with ethylenically unsaturated monomers, preferably those with vinyl functionality like styrene, methylstyrene, and methyl methacrylate, i.e. the classical way of crosslinking via radical copolymerization using conventional initiators like benzoyl peroxide or methyl ethyl ketone peroxide and conventional accelerators like cobalt octoate and inhibitors like p-benzoquinone.
WO-A-00/06632 describes composite materials based on renewable resources. The components of the resin matrix are ring opening products made from epoxidized fatty substances and unsaturated short chain carboxylic acids and/or anhydride-modified fatty acids.
U.S. Pat. No. 6,121,398 describes the use of hydroxylated plant or animal oil which is maleinized and copolymerized with a vinyl group-containing reactive monomer such as styrene or methylstyrene. Said oil is used as a basis to form molding compounds together with artificial or natural fibers. High values of tensile strength and tensile modulus can be reached by using woven glass fiber mats.
In WO-A-97/02307 a polymeric material based on renewable raw materials has been described which is based on 10-90 wt. % of a triglyceride having at least two epoxy and/or aziridine groups and 5-90 wt. % of a polycarboxylic acid anhydride with 0.01-4 wt. % of a polycarboxylic acid. From the chemical point of view it belongs to the class of aliphatic epoxy resins and it possesses properties similar to those of common thermosetting resins. In the curing process of these resins, which may be described by the reaction sequence depicted in Scheme 5 below, small amounts of (poly)carboxylic acids adopt the function of a reaction starter or initiator. Since the epoxy groups of an epoxidized triglyceride are relatively unreactive, the curing process requires high temperatures of e.g. 130 to 180° C. The resulting substances are polyesters, the properties of which depend to a great extent on the fatty-acid spectrum of the native oils employed. Also disclosed is the use of such polymeric materials in combination with inorganic fillers like carbonates, flame retardant fillers such as aluminum trihydroxide, fibers like flax or glass, and also organic fillers based on renewable resources like sawdust, straw, wool, and the like and the application of such polymeric materials in pultrusion and wet molding processes. Such polymeric materials are commercially available under the trade name PTP®.

In the above scheme, R1 at each occurrence independently forms an optionally epoxidized fatty acyl group together with the adjacent carbonyl group. The epoxy moieties (or the moieties formed in their reaction with the carboxylic acids or anhydrides) and the carbonyl groups of the triglyceride acyl groups are usually separated by one or more saturated or unsaturated carbon atoms which have been omitted for simplicity of illustration R2 at each occurrence independently is preferably selected from the group consisting of saturated and unsaturated C1-40 aliphatic moieties and aryl groups, bearing at least one additional carboxy group and optionally being further substituted with hydroxy, oxo or alkoxycarbonyl groups; and R3 preferably represents either two monovalent moieties independently selected from optionally substituted saturated and unsaturated C1-10 aliphatic groups, or a bivalent moiety which, together with the adjacent carbon atoms, forms an alicyclic, aromatic or heteroaromatic ring or an alicyclic or aromatic bi- or polycyclic ring system.
The reaction of epoxide moieties with polycarboxylic anhydrides is depicted in more detail in Scheme 6 below.

In Scheme 6, R1 and R2 independently are organic moieties, preferably forming together with the epoxide moiety an epoxidized triglyceride as indicated above, and R3 is as described above for Scheme 5.
However, apart from these examples, thermosetting biopolymers—either native or formed by polymerization of native monomers—are still very rare compared to the wide variety of thermoplastic biopolymers.
Under the threat of a global climate change there is a need for materials which are neutral in CO2 emission over their life. A well-known example is the increasing use of composites comprising natural fibers like hemp, flax, or jute in the interiors of motor vehicles. There is also increasing interest in composite materials comprising resins and binding agents which can be obtained from renewable raw materials.
However, in the field of thermosetting composites for industrial applications up to now only resins of petrochemical origin like unsaturated polyester (UP) and vinyl ester (VE) resins are being used. These resins are not CO2 neutral with regard to their life cycle and will therefore fall under the limitations of incineration stipulated in recent waste management legislation.
It is therefore an object of the present invention to provide a SMC, TMC and BMC comprising a resin based on renewable resources. Parts molded from such an SMC, TMC and BMC could possibly be incinerated or even composted without contributing to the increase of atmospheric carbon dioxide as the resins have been formed—at least to a very large extent—by renewable materials.
As mentioned above, conventional SMC, TMC or BMC based on VE or UP resins leads to emissions of volatile organic compounds (VOC) such as styrene, thus posing a potential risk to the health of the end-user of the product, i.e. the molded part, and the people getting in contact with the intermediate product, i.e. the uncrosslinked SMC, TMC or BMC during the production of both the molded part and the SMC, TMC or BMC itself.
It is therefore another object of the present invention to provide a SMC, TMC and BMC without emission of volatile organic compounds (VOC) of petrochemical origin.
As described above, the maturation or thickening process is the decisive step in SMC, TMC and BMC production as only by thickening the liquid and/or sticky resin adopts a consistency allowing to handle the material in an industrial process Viscosities of 5×104 to 1×105 Pa s are necessary or typical. However, the classical thickening reaction with alkaline earth oxides and/or hydroxides cannot be carried out in resins based on renewable resources.
It is therefore still another object of the present invention to provide a SMC, TMC and BMC comprising a resin based on renewable resources which can accomplish a reaction that, after a certain maturation time, leads to a viscosity level providing a SMC, TMC and BMC where the carrier film can be removed without resin sticking to the film and/or the hands of the operator.
In conventional SMC, TMC or BMC based on UP or VE resins the viscosity of the matrix is lowered in the molding process due to the influence of temperature and pressure. This behavior is important as it allows the SMC, TMC and BMC to fill the cavity of the mold within the short time of the molding process.
It is therefore an object of the present invention to provide a SMC, TMC and BMC comprising a resin based on renewable resources which shows a mold flow behavior similar to that of a SMC, TMC and BMC based on UP or VE resins.
Shelf life of SMC, TMC and BMC after maturation is a very important property. In practice SMC, TMC and BMC need a shelf life of at least several weeks as the material has to be shipped to the customer and it must be possible to store the material at the customer's location for a certain period of time, during which the key properties of the material have to remain essentially the same.
As it is known that moisture adversely affects the stability of some uncured resins based on renewable resources such as PTP resin, it is also an object of the present invention to provide a SMC, TMC and BMC based on renewable resources which is not susceptible for curing by moisture which is contained in the formulation or which migrates into the material during storage.
It is another object of the present invention to provide a SMC, TMC and BMC comprising a resin based on renewable resources which can be processed in a SMC, TMC or BMC process which is basically identical with the process which is used to produce SMC, TMC or BMC based on unsaturated polyester (UP) resins or vinyl ester (VE) resins and which can be used in molding process similar to standard SMC, TMC or BMC molding process leading to molded parts with mechanical properties comparable to those obtained with standard SMC, TMC or BMC.
In prior art the use of modified triglycerides from plant oils together with glass fiber or natural fiber mats for the production of molding compounds with high tensile modulus is described. Apart from the fact that complex geometries of molded parts cannot be realized with woven mats, molds had to be heated for several hours which is much too long for the production of parts in an industrial process.
It is therefore an object of the present invention to provide a SMC material comprising a resin based on renewable resources and cut glass fibers with a length of 25 mm and/or 50 mm with which complex geometries in molded parts can be realized in molding times not exceeding several minutes.
Additionally, it is an object of the present invention to provide such an SMC, TMC and BMC having mechanical properties such as tensile strength/tensile modulus and flexural strength/flexural modulus comparable to those of SMC, TMC or BMC based on conventional UP and VE resins.
In SMC, TMC or BMC based on UP or VE resins, internal mold release agents are used to enable or facilitate demolding of the molded part Common mold release agents are metal stearates like zinc stearate or calcium stearate which have been used in SMC, TMC or BMC based on UP or VE resins for decades, but mold release agents on the basis of surface active substances and polymers are also known.
It is therefore a further object of the present invention to provide a SMC, TMC and BMC comprising a resin based on renewable resources which is compatible with common internal mold release agents.
As described above, compounds or composites based on renewable resources can mostly be considered as thermoplastic compounds in the sense of the definition given in German Industry Standard DIN 7742 part 2. It is known from conventional compounds—i.e. those based on polymers of petrochemical origin—that the mechanical properties of fiber reinforced thermosetting compounds like SMC, TMC and BMC are better than those of fiber reinforced thermoplastic materials like long fiber reinforced thermoplastics (LFT) and glass mat reinforced thermoplastics (GMT).
It is therefore a further object of the present invention to provide a SMC, TMC and BMC based on resins from renewable resources that possesses mechanical properties superior to those typical for thermoplastic fiber reinforced plastics.
According to the invention, these objects are achieved by the SMC, TMC and BMC compounds of claim 1.
It has been found that resin systems based on triglycerides having at least two epoxy groups, polycarboxylic anhydrides, and polycarboxylic acids have a viscosity suitable to use these resins in a SMC, TMC or BMC process, i.e., in such a way that the impregnation of the glass fiber rovings is on the same level as known from conventional SMC, TMC or BMC based on UP or VE resins. Since no vinyl group-containing monomers such as styrene are used in these resin systems, such monomers do not contribute to their organic emissions (VOC). Here and hereinbelow, the term “polycarboxylic acid” is to be understood to encompass any carboxylic acid having at least two carboxy groups. Accordingly, the term “polycarboxylic anhydride” is to be understood to encompass any anhydride derived from a polycarboxylic acid by intramolecularly forming one or more anhydride moieties from one or more pairs of carboxy groups.
It has further been found that the addition of epoxides with at least one terminal epoxy group or cycloaliphatic or heterocyclic compounds with one or more epoxy groups per molecule to mixtures of epoxidized triglycerides with at least two epoxy groups per molecule, polycarboxylic anhydrides, and polycarboxylic acids, which are known to undergo crosslinking reactions only at elevated temperatures, leads to resin pastes that can undergo a thickening reaction at room temperature and thus be used in a SMC, TMC or BMC application. It is also possible to use epoxides having both types of epoxy groups, or mixtures of two or more of the above additional epoxides. Epoxides with terminal epoxy groups may be glycidyl ethers or esters, such as 1,4-cyclohexanedimethanol diglycidyl ether or glycidyl laurate, or may be produced by epoxidizing compounds containing vinyl groups or other terminal carbon-carbon double bonds. Suitable cycloaliphatic or heterocyclic epoxides may belong to the group of epoxidized cycloaliphatic or heterocyclic compounds with 4 to 7 ring atoms.
The reaction of cycloaliphatic diepoxides with polycarboxylic anhydrides is depicted in Scheme 7 below.

In Scheme 7, R1 may be any divalent organic moiety, such as an alkylene or —CH2—OC(═O)— group while R2 has the same meaning as R3 in Schemes 5 and 6 above.
Terminal epoxides having additional reactive functional groups, such as (3-glycidyloxypropyl)-trimethoxysilane, may also be fixed on suitable carrier materials, as depicted in Scheme 8 below.

In Scheme 8, R1 may be any organic or inorganic group that can react with a hydroxy group to form an oxygen-silicon bond. Preferably, R1 is a lower alkoxy group such a methoxy or a halogen such as chlorine. R2 and R3 are preferably lower alkyl or alkoxy groups such as methyl or methoxy. R4 may be any divalent organic moiety, preferably an optionally oxygen-interrupted alkylene group and most preferred a —(CH2)3—O—CH2— group.
Thickenable resins suitable for a SMC, TMC or BMC application can also be obtained by the use of primary and secondary amines or quaternary ammonium compounds or C—H-acidic compounds in addition to the terminal, cycloaliphatic or heterocyclic epoxides mentioned above. Basically, all primary and secondary amines with at least two amine groups can be used. These can also be fixed on suitable carrier materials by ion exchange or by chemical reactions forming a covalent bond. Preferably, carrier materials from the group of silicates, especially layered silicates can be used. Also preferred are amines which are obtained by the introduction of at least two amino groups in the side chains of a triglyceride. Preferred is the introduction of primary and secondary amine groups. These can additionally be reacted with electrophilic agents with at least two functional groups during the maturation or thickening of the resin paste. Preferred are such electrophilic agents that can be obtained on the basis of renewable resources especially polyepoxides with at least two terminal epoxy groups as they can be obtained e.g. from phenolic containing or resorcinol containing substances of natural origin like e.g. cashew nutshell oil.
From the group of quaternary ammonium compounds basically all quaternary ammonium compounds can be used that possess at least one quaternary ammonium group. Preferred are alkyl quaternary ammonium compounds, more preferred are ammonium salts of mono- or polycarboxylic acids.
Quaternary ammonium salts can also be fixed on suitable carrier materials, e.g. by ion exchange. Preferred carrier materials are those mentioned above.
A proposed mechanism for the reaction between primary or secondary amines or amides, polycarboxylic anhydrides and epoxides is depicted in Scheme 9 below.

In Scheme 9, R1 may be hydrogen or hydrocarbyl, R2 has the same meaning as in Scheme 7 above, R3 may be hydrocarbyl or acyl, or R1 and R3 together with the azanediyl (NH) group form a saturated or unsaturated mono- or polycyclic system, and R4 and R5 have the same meanings as R1 and R2 in Scheme 6 above.
According to the invention, there is provided a resin paste for the application in a sheet molding compound, a thick molding compound or a bulk molding compound, said resin paste comprising                (a) 30 to 95 parts by weight of at least one epoxidized triglyceride having at least two epoxy groups,        (b) 5 to 90 parts by weight of at least one polycarboxylic anhydride,        (c) 0.001 to 20 parts by weight of a polycarboxylic acid,        (d) 0.1 to 40 parts by weight of at least one terminal, cycloaliphatic or heterocyclic epoxy compound, and        (e) 0 to 40 parts by weight of a composition comprising at least one compound selected from the group consisting of quaternary ammonium compounds, primary amines, secondary amines, carboxamides, N-substituted carboxamides, epoxidized alkoxysilanes, C—H-acidic compounds and mixtures thereof.        
Preferably, the relative amounts of components (a) through (e) are such that the parts by weight add up to 100.
As epoxidized triglyceride, any compound obtainable by epoxidizing at least two double bonds of a triglyceride having two or more double bonds in its acyl moieties can be used. The two or more epoxidized double bonds may be present in only one, in two, or in each of the three acyl moieties of the triglyceride. As the epoxidized triglycerides are derived from naturally occurring triglycerides which in turn are usually derived from mixtures of fatty acids of various chain lengths and degrees of unsaturation, the number and position of epoxy groups may vary from molecule to molecule. Non-limiting examples of suitable naturally occurring triglycerides are fats and fatty oils such as soya oil, linseed oil, perilla oil, tung oil, oiticica oil, safflower oil, poppy oil, hemp oil, cottonseed oil, sunflower oil, rape oil, euphorbia iagascae oil, euphorbia lathyris oil, peanut oil, olive oil, olive seed oil, almond oil, kapok oil, hazelnut oil, apricot seed oil, beechnut oil, lupine oil, maize oil, sesame oil, grapeseed oil, lallemantia oil, castor oil, oils of marine animals such as herring oil, sardine oil, menhaden oil or whale oil, or mixtures of any of the preceding. A particularly preferred epoxidized triglyceride is epoxidized linseed oil.
In a preferred embodiment, the resin paste comprises 40 to 70 wt. %, more preferably 45 to 60 wt. % of the at least one epoxidized triglycerides.
All amounts given in percent by weight (wt. %) here and below are based on the sum of the amounts of components (a) to (e) as 100 wt. %.
As polycarboxylic anhydrides, any anhydrides formed by intramolecular water elimination of polycarboxylic acids (cf. below) may be employed. These may be derived from acyclic polycarboxylic acids such as maleic anhydride (from maleic acid) or succinic anhydride (from succinic acid), or from cyclic or polycyclic non-aromatic, aromatic or heteroaromatic polycarboxylic acids, such as phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophibalic anhydride, trimellitic anhydride, pyromellitic dianhydride, 1,2-, 2,3- and 1,8-naphthalic anhydrides, 1,4,5,9-napthalenetetracarboxylic dianhydride, quinolinic anhydride, diphenic anhydride, norbornenedicarboxylic anhydride, and any mixtures or substitution products thereof Tetrahydrophthalic anhydride is preferred. Particularly preferred are such polycarboxylic anhydrides which are liquid at room temperature like methylhexahydrophthalic anhydride, methylendomethylentetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and citraconic anhydride.
In a preferred embodiment, the resin paste comprises 25 to 45 wt. %, more preferably 30 to 40 wt. % of the at least one polycarboxylic anhydride.
Polycarboxylic acids include, without being limited thereto, citric acid, polymerized tall oils, azelaic acid, gallic acid, dimerized or polymerized oleoresin acids, dimerized or polymerized anacardic acid, cashew nut shell liquid, polyuronic acids, polyalginic acids, aromatic polycarboxylic acids such as mellitic acid, pyromellitic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid and terephthalic acid, substituted aromatic polycarboxylic acids such as methylphthalic acid, di- and polycyclic aromatic polycarboxylic acids such as naphthalenedicarboxylic and naphthaleneteracarboxylic acids, mono-, bi- and polycyclic cyloaliphatic polycarboxylic acids such as cyclopropane-, cyclobutane-, cyclopentane- and cyclohexanedicarboxylic acids or tetrahydrophtbalic acid, heterocyclic polycarboxylic acids such as pyridinedicarboxylic acids, open-chain polycarboxylic acids such as oxalic, malonic, succinic, glutaric, adipic, maleic or fumaric acid, and any substituted congeners or mixtures of the preceding. Among these, dicarboxylic and tricarboxylic acids are preferred A particularly preferred polycarboxylic acid is citric acid.
In a preferred embodiment, the resin paste comprises 0.01 to 10 wt. %, more preferably 0.05 to 2 wt. % of the at least one polycarboxylic acid.
As terminal, cycloaliphatic or heterocyclic epoxy compounds, epoxides with at least one terminal epoxy group or cycloaliphatic or heterocyclic compounds with one or more epoxy groups per molecule may be employed. It is also possible to use epoxides having both types of epoxy groups, or mixtures of two or more of the above additional epoxides. Epoxides with terminal epoxy groups may be glycidyl ethers or glycidyl esters, such as 1,4-cyclohexanedimethanol diglycidyl ether or glycidyl laurate, or silicon compounds such as (3-glycidyloxypropyl)trimethoxysilane, which may also be bound to a suitable carrier, or may be produced by epoxidizing compounds containing vinyl groups or other terminal carbon-carbon double bonds. Suitable cycloaliphatic or heterocyclic epoxides may belong to the group of epoxidized cycloaliphatic or heterocyclic compounds with 4 to 7 ring atoms. Most preferred cycloaliphatic epoxides are those having at least one epoxidized cyclohexane ring, such as 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexanecarboxylate, or epoxidized terpene hydrocarbons, such as limonene dioxide. Further preferred epoxides are those which can be obtained from renewable resources, such as modified triglycerides having terminal epoxy groups, e.g. the products obtained by esterifying hydroxylated triglycerides with acrylic acid and epoxidizing the acrylate intermediate, or epoxidized products of the metathesis of unsaturated fatty acid alkyl esters with ethene as described by S. Warwel in Chemosphere, 2001, 43, 39.
Particularly preferred are epoxy compounds which are liquid at room temperature.
In a preferred embodiment, the resin paste comprises 0.1 to 20 wt. %, more preferably 5 to 10 wt. % of the at least one terminal, cycloaliphatic or heterocyclic epoxy compound.
As quaternary ammonium compounds, basically all quaternary ammonium compounds can be used, quaternary alkylammonium compounds being preferred. More preferred are quaternary ammonium compounds which are obtainable from natural resources, such as the quaternization products of fatty amines, e.g. stearyl trimethyl or cetyl trimethyl ammonium compounds.
As primary or secondary amines, basically all compounds having at least one primary and/or secondary amino group can be used. Suitable amines include, without being limited thereto, acyclic aliphatic amines such as alkyl- or dialkylamines, alicyclic amines such as cyclohexylamine or dicyclohexylamine, aromatic amines such as aniline or substituted anilines, and heterocyclic amines such as piperidine, morpholine or imidazole. More preferably, the primary or secondary amine or mixture of amines has at least two amino groups, such as ethylene diamine, 1,6-diaminohexane or piperazine. The amines may also have additional functional groups, such as alkoxycarbonyl groups like methyl 10-aminodecanoate. More preferably, the amines are derived from natural products, such as fatty amines or aminotriglycerides. Especially preferred are amines which are liquid at room temperature.
As carboxamides or N-substituted carboxamides, any compounds having at least one carboxamido group with at least one hydrogen attached to the amide nitrogen can be used, including urethanes and ureas.
As epoxidized alkoxysilanes, compounds such as (3-glycidyloxypropyl)trimethoxysilane or substitution or coupling products thereof may be used.
Suitable C—H-acidic compounds include, without being limited thereto, p-dicarbonyl compounds, for example β-ketoesters, such as alkyl acetoacetates or alkyl benzoylacetates, β-diketones, such as acetylacetone, and derivatives of malonic acid such as malonates, Meldrum's acid and malonodinitrile.
In a preferred embodiment, the component (e) comprises at least one quaternary ammonium compound
In another preferred embodiment, the component (e) comprises a primary or secondary amine or a mixture of two or more primary and/or secondary amines.
In still another preferred embodiment, the component (e) comprises an epoxidized alkoxysilane.
In yet another preferred embodiment, the component (e) comprises at least one C—H-acidic compound.
Preferably, at least one of the compounds of component (e) is adsorbed on or covalently bound to a carrier material. More preferably, the carrier material is selected from the group consisting of layered silicates, such as vermiculite or montmorillonite, silica, such as quartz or cristobalite, glass, and mixtures thereof.
According to the invention, there is also provided a molding compound comprising the resin paste as described above, reinforcing fibers, and, optionally, one or more additional ingredients selected from the group consisting of thermoplasts, such as polyethylene, initiators, inhibitors, mold release agents, such as calcium stearate, fillers, such as aluminum hydroxide or calcium carbonate, nanofillers, such as barium sulfate, absorbents, such as molecular sieves, processing additives, wetting and dispersing additives, air release additives, shrinkage modifiers, and colorants.
In a preferred embodiment, the reinforcing fibers are glass fibers,
Another object of the invention is a molded article comprising a reaction product of the components of the above SMC, BMC or TMC molding compounds.
According to the invention, there is also provided a process for preparing a sheet molding compound, a thick molding compound or a bulk molding compound, said process comprising impregnating reinforcing fibers with a resin paste comprising                (a) 30 to 95 parts by weight of at least one epoxidized triglyceride having at least two epoxy groups,        (b) 5 to 90 parts by weight of at least one anhydride of a polycarboxylic acid,        (c) 0.001 to 10 parts by weight of a polycarboxylic acid,        (d) 0.1 to 40 parts by weight of at least one terminal, cycloaliphatic or heterocyclic epoxy compound,        (e) 0 to 40 parts by weight of a component comprising at least one compound selected from the group consisting of quaternary ammonium compounds, primary amines, secondary amines, carboxamides, N-substituted carboxamides, epoxidized alkoxysilanes, C—H-acidic compounds and mixtures thereof,said resin paste optionally being admixed with one or more additional ingredients selected from the group consisting of thermoplasts, initiators, inhibitors, mold release agents, fillers, absorbents, processing additives, wetting and dispersing additives, air release additives, shrinkage modifiers, and colorants,to obtain a resin-fiber intermediate product and maturing said intermediate product for a time sufficient to obtain a non-sticky compound suitable for sheet molding, for thick molding or for bulk molding.        
In several preferred embodiments of the process the composition of the resin paste employed in the process corresponds to the preferred compositions described above for the resin paste itself.
Still another object of the present invention is a molded article obtainable by molding a molding compound obtained according to the above process under elevated pressure at 120 to 200° C.
As the chemistry of resins based on renewable resources in general is completely different from that of SMC, TMC and BMC based on UP or VE resins, also the thickening reaction is completely different in terms of its chemical nature. Accordingly, one would not assume to achieve the same behavior in the thickening reaction. However, it was surprisingly found that it is possible to achieve a thickening behavior in resins based on epoxidized plant oils that is similar to the thickening behavior of UP or VE resins in conventional SMC, TMC or BMC. A shelf life or processability of several weeks which is important for the applicability of the material in practice can also be achieved.
Surprisingly it was now found that mold flow behavior of SMC, TMC and BMC based on resins made from epoxidized plant oils is also comparable to that of conventional SMC, TMC and BMC in spite of the fact that the thickening reactions are completely different from those in conventional SMC, TMC and BMC based on UP or VE resins.
Additionally, it was surprisingly found that glass fibers which are conventionally used in the production of SMC together with unsaturated polyester (UP) and vinyl ester (VE) resins and that possess sizings compatible with these UP and VE resin systems can be used together with the resin systems based on renewable resources as according to the invention. In spite of the sizing on the glass fiber and the resin being completely different in chemical nature and not being adapted to each other, the dispersion of the glass fibers in the resin is very good and fiber/matrix interaction is on a level that leads to mechanical properties of the compound that are comparable to those of conventional SMC based on UP resins.
Surprisingly it was also found that the resins used in the present invention are perfectly compatible with conventional mold release agent from the family of metal stearates.
The invention is illustrated in more detail by the following non-limiting examples showing exemplary embodiments.